A. Ring Cans
Conventional metal containers, particularly paint containers and the like used by the consuming public are cylindrical in shape, and typically comprise a container body, a bottom plate closing one end of the container, a ring which is secured to the open end of the container and a lid or a plug which fits into the ring to close the container. Reference may be had to U.S Pat. No. 4,421,247 to Lombardo et al for a typical example showing the plug and ring construction and the fit therebetween.
The cylindrical container body is usually formed from a rectangular flat piece of sheet metal rolled into a cylinder with the sides joined together by a continuous soldered side seam and a circular bottom plate is then attached, usually by a crimped double seam, to one of the open ends of the cylinder. At the other end of the cylinder, an annular, grooved ring member is similarly attached. Various types of seams can be used and some container are simply drawn or stamped into a one piece container body although the seamed construction described is widely used.
Paint containers of the type described have proven acceptable for their intended function and use. There are, however, a number of drawbacks which are principally centered about or arise because of the ring and plug construction described.
From the viewpoint of a can manufacturer, the ring is an unnecessary appendage which, if removed, would materially simplify the container. That is the container could be manufactured with less metal. The container could also be manufactured quicker and more easily because making the ring and then seaming the ring to the container's side wall opening would not be required. Thus, if the ring could be eliminated, the cost of the container would materially decrease.
From the consumer's viewpoint, the ring is undesirable because, despite several patented concepts to the contrary, the ring collects paint and prevents the container from being resealed in an air-tight manner. The ring also inhibits the ability of the user to pour the contents of the container. The ring also prevents all the contents of the container from being emptied.
A less obvious drawback of the plug-ring design is that stacking or nesting of the containers, one on top of the other, cannot occur with conventional designs. Stacking is important from both a shipping and dealer inventory standpoint. Such a feature is simply not readily available with conventional designs because the ring sealing grooves interfere with or prevent the formation of a plug or lid which can function as an interlocking member.
Within the container art, the ring is viewed as a necessary evil which is required to meet the stringent requirements of the paint industry so that, at least initially, an air-tight, shock resistant seal is achieved for the container body. Inherent in the ring-plug seal approach is the elimination of any problems which might otherwise result in attempting to seal, in a repeatable manner, a soldered seam. That is the container is rolled and maintained in a cylindrical shape by a longitudinal soldered seam which extends the entire length of the container. More precisely, each longitudinal end of the container is formed as a "U" and the ends are interlocked, crimped and soldered. The soldered seam is thus four times the thickness of the metal. By crimping the ring to the open end of the container and over the soldered seam permits the plug to be sealed within seamless grooves formed in the ring. The ring-plug seal is taught in the container art as being effective because of the multiplicity of sealing surfaces. In practice, it is believed that the ring-plug closure initially operates as a seal because i) there is no soldered seam to seal and ii) an interference fit is established between the ring and the plug. That is, as the plug is wedged into the ring, various interference fits are formed by opposing wedge angles between the plug and ring which permanently deform the metal so that the lid is prevented from popping off when the container is dropped. Inherently, the effectiveness of the interference fit is diminished once the plug is removed from and then reapplied to the ring since the metal has already undergone a plastic deformation.